Response Of Farmland Greenhouse Gas Emissions To Deficit Irrigation Based On APSIM Model

Nitrous oxide?N₂O?is a gas with a long-term existence and a large greenhouse effect.Its emissions are closely related to irrigation and nitrogen application measures in farmland.High water and high nitrogen will increase N₂O emissions from farmland soil while increasing production,which is not conducive to the sustainable development of agriculture.Need to optimize farmland management measures to find a reasonable nitrogen reduction irrigation model.In this study,the winter wheat-summer maize in Yangling area was used as the research object,and the field test data from 2016 to 2018 was used to verify the APSIM model.The verified APSIM?Agricultural Production Systems Simulator?model was used to simulate the two scenarios.The first scenario design was based on the field experiment from2017 to 2018 for a 20-year crop rotation simulation,and the climate data were repeated from2017 to 2018 for 20 years.Six nitrogen fertilizer gradients were set,N50?50 kg/hm²?,N100?100 kg/hm²?,N150?150 kg/hm²?,N200?200 kg/hm²?,N250?250 kg/hm²?and N300?300kg/hm²?.The second scenario design analyzes the 30-year?1984?2013?precipitation data in Yangling area,finds the typical years of dry years,normal years and wet years,and uses the typical year meteorological data for 20-year rotation,which is the typical year Repeated for20 years,set irrigation to 100%W?crop water demand?for high water treatment,80%W for medium water treatment,and 60%W for low water treatment.If rainfall meets the crop water demand,no irrigation will be carried out.Nitrogen fertilizer is set with 4 gradients N100?100 kg/hm²?,N150?150 kg/hm²?,N200?200 kg/hm²?and N250?250 kg/hm²?.The design of both scenarios is the repetition of meteorological data,with the aim of exploring the long-term effects of agricultural practices on crop yield,water use efficiency and N₂O emissions.The main conclusions are as follows:?1?After the directly calibration of parameters relating to change soil organic carbon based on the previous research,we conducted calidity test on APSIM using the experimental data at Yangling,and the results showed that the calibrated model can well simulated yield?R²?0.84?,soil water?R²?0.76?and N₂O emissions?R²?0.84?.?2?Under the first Scenario design condition,When the nitrogen application rate of each crop is not higher than 200 kg/hm²,in the long-term rotation,deficit irrigation cannot significantly reduce soil N₂O emissions,but in the high nitrogen application rate above 200kg/hm²,severe water deficit at the seedling stage is conducive to N₂O emission reduction.Under the water deficit treatment,the optimal nitrogen application rate for the winter wheat-summer corn rotation system is 150 kg/hm² per crop.At this time,except for the TI treatment,the total yield and water use efficiency of the other treatment rotations reached the peak.When the nitrogen application rate is 150 kg/hm² per crop,the water use efficiency WUE of T4 treatment with moderate water deficit at seedling stage and jointing stage is 2.37kg/m3,which is significantly higher than other treatments,and the total yield is slightly lower than the full irrigation Treatment,and the N₂O emission intensity is not significantly different from other treatments?except for TI treatment?,so this study believes that T4treatment is the best when the nitrogen application rate is 150 kg/hm² per crop.?3?Under the second Scenario design condition,deficit irrigation in dry years,normal years and wet years can reduce N₂O emissions,but the difference isn't significant when the nitrogen application rate is less than 200kg/hm².In addition,deficit irrigation can improve WUE,but also reduce yield.The combined effect of water and nitrogen fertilizer in dry years is obvious.When the nitrogen application rate is 150 kg/hm² per crop,low water treatment is the best.At this time,the N₂O emissions from low water treatment are not significantly different from those of medium water and high water treatment.The water use efficiency is significantly higher than that of medium water and high water treatment,and there is no significant difference in yield between the various water treatments.When the amount of nitrogen applied is 200 kg/hm²per crop,medium water treatment is more advantageous.At this time,there is no significant difference in N₂O emission intensity and water use efficiency between medium water treatment and low water treatment,The yield of medium water treatment is significantly higher than that of low water treatment,and there is no significant difference between the yield of medium water treatment and high water treatment.?2?The treatment of low and medium water in normal years is significantly better than that of high water treatment.When the nitrogen application rate is 200 kg/hm² per crop,low water treatment is the best;at this time,the total yield of low water treatment rotation is not significantly different from the total yield of medium water and high water rotation,but the N₂O emissions are significantly lower Medium water and high water treatment;water use efficiency is significantly higher than high water treatment.When the nitrogen application rate is 250 kg/hm² per crop,the medium water treatment is the best;the total yield of the medium water treatment rotation is significantly higher than that of the low water treatment,and there is no significant difference from the high water treatment;the water use efficiency is significantly higher than the high Water treatment;N₂O emission intensity is not significantly different from low water.?3?In high water years,low water treatment is the most suitable.At this time,summer maize has sufficient precipitation and sufficient soil water storage,which provides water support for the growth and development of winter wheat.The nitrogen application rate is200 kg/hm2 is better.There is no significant difference between the total rotation yield and the nitrogen application rate of 250 kg/hm²,but the N₂O emission and emission intensity are significantly lower than that of 250 kg/hm² nitrogen application.Consideration the economic and environmental effects of winter wheat-summer maize rotation,this study believes that the nitrogen application rate per crop is 150?250 kg/hm²,and low water and medium water treatments are preferably.Water shortage during the growing period should be given priority to the seedling period.